This allows the existing code passing wxStockCursor instead of wxCursor
parameter to keep working with the functions taking wxCursorBundle
instead of wxCursor too and, in particular, we can keep just a single
version of wxSetCursor() instead of having two overloads (which wasn't
necessarily a problem for just this function, but is inconsistent with
the other functions taking wxCursor, notably wxDropSource ctor where
overloads really can't be used because we would need too many of them
to cover all combinations of 3 different wxCursor parameters).
It didn't make sense to include wx/utils.h from wx/cursor.h, but it
somewhat does make sense to declare busy cursor-related functions and
wxBusyCursor itself in this header, so extract these declarations into
their own header which is included from both wx/cursor.h and wx/utils.h
for compatibility, but can be also included directly.
Document that wx/cursor.h doesn't pull in wx/utils.h any longer as it's
an incompatible change (but hopefully one not resulting in too much
disruption and so worth it).
Vadim Zeitlin